The disclosure relates generally to an optical transmission system and more particularly to an optical transmission system having low nonlinear optical effects. The transmission system is particularly applicable for long haul submarine transmission applications.
In long haul submarine transmission applications, it is not possible to transmit optical signals over very long distances without amplification due to attenuation. Accordingly, long haul submarine optical transmission systems include amplifiers repeated at certain distances along the length of the system. Because amplification equipment adds to the expense of the system, it is desirable to have as few amplifiers as possible per system length, while at the same time not adversely affecting the signal transmission characteristics of the system.
One possible strategy for reducing the number of amplifiers in a given system is to increase the amount of power launched into to the fiber at each amplification site. However, increasing the launch power above a certain threshold level for a given fiber (or combination of fibers) increases nonlinear optical effects such as four-wave mixing (FWM) and cross-phase modulation (XPM), such that optical signal transmission through long-haul optical networks becomes unsatisfactorily degraded. While dispersion reduces nonlinear effects such as FWM and XPM, the interplay of the accumulation of large amounts of chromatic dispersion and self-phase modulation (SPM) creates noise and distortion in the optical system.
Accordingly, a need exists for alternative long haul optical fiber transmission systems having increased length between amplifiers without adversely affecting the signal transmission characteristics of the system to unsatisfactory levels.